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Why would you name a muscle after its supposed function when its function is actually something totally different? Probably due to what made sense from how it looked, not by how it acted. Of course, we are talking about the abductor hallucis.

Think about all the anatomy you have learned over the years. Think about all the taxonomy and how it was done: sometimes by thename of the discoverer and more often by its anatomical location. The abductor hallucis seems to be the latter.

The abductor and adductor hallicus function from approximately midstance to pre swing (1-4) (toe off), applying equal and opposite rotational vectors of force (in an ideal world) of the proximal phalynx of the hallux. This should resolve into a purely compressive force (5). In a closed chain environment, the transverse head of the adductor hallicus should act to prevent “splay” of metatarsals, along with the lumbricals and interossei (6), providing stabilzation of the forefoot (7) and rearfoot (8) during preswing, while the oblique head serves to help maintain the medial longitudinal arch.

The abductor hallicus is actually a misnomer, as it most cases it is not an abductor but rather a plantar flexor of the 1st ray, particularly the proximal hallux, (assisting the peroneus longus) and supinator about the oblique midtarsal joint axis (5). In the majority of cases, there doesn’t appear to be a separate, distinct insertion of the adductor hallicus to the base of the proximal phalynx, but rather a conjoint insertion with the lateral head of the flexor hallicus bevis into the lateral sesamoid and base of the proximal phalynx (9-11), emphasizing more of its plantar flexion function and stabilizing actions, rather than abduction.

In one EMG study of 20 people with valgus (12) they looked at activity of adductor and abductor hallucis, as well as flexor hallucis brevis and extensor hallucis longus. They found that the abductor hallucis had less activity than the adductor. No surprise here; think about reciprocal inhibition and increased activity of the adductor when the 1st ray cannot be anchoroed. They also found EMG amplitude greater in the abductor hallucis by nearly two fold in flexion.

So, the abductor hallucis seems to be important in abduction but more important in flexion. Either way, it is a stance phase stabilizer that we are beginning to know a lot more about. As for the name? You decide...

When it comes to gait, getting the 1st ray to the ground is the name of the game. When weight travels through the medial forefoot and we are able to push off the 1st ray complex, that is called "high gear push off". This was 1st discussed F Bojsen-Møller in this excellent paper (1), that just happens to be a free full text! Craig Payne, The Running Research Junkie has offered and excellent commentary on the topic here as well.

High Gear Push Off can happen when 3 conditions are met:

we have a intact visual, vestibular and kinesthetic systems that ensure we can remain upright in the gravitational plane.

we have an intact calcanocuboid locking mechanism

we have adequate skill, endurance and strength of our extensor hallucis brevis

The 1st condition is more global and ensures that our cerebellum and vestibular apparatus are playing nice together to create balance, of the literal sort, We seek to keep our visual axes parallel and our center of gravity over our foot. Remember that the BODY will move itself AROUND the visual axes. If the axes are off, the brain will tilt the head and the body will move AROUND the head to accommodate. We have talked about that in these posts here on the blog.

The 2nd condition, the calcaneo-cuboid locking mechanism, works in the coronal plane and relies on a functioning peroneal group, where the peroneus longus and brevis wrap around the lateral malleolus, cuboid and tail of the 5th metatarsal, crossing the foot diagonally to insert on the base of the 1st metatarsal. When working properly, its actions will be to plantar flex and everting the forefoot, lowering the 1st ray complex down and assisting the shift of the center of gravity more medial for the weight to pass through the medial foot and out through the hallux (ideally).

The 3rd condition, the ability to descend the 1st ray, relies on the actions of the peroneus, appropriate supination of the forefoot and ability of the extensor hallucis brevis to do its job. Because the tendon travels behind the axis of rotation of the 1st metatarsal phalangeal joint, in addition to providing extension of the proximal phalynx of the hallux, it can also provide a downward moment on the distal 1st metatarsal (when properly coupled to and temporally sequenced with the flexor hallicus brevis and longus). If the axis of motion for the 1st metatarsal phalangeal joint moves posteriorly, to behind (rather than under) the joint, the plantar pressures increase at MTP’s 4-5 and decrease at the medial mid foot, moving you into low gear push off. If moved even further posteriorly, the plantar pressures, and contact time in the mid foot and hind foot (2). For more on the extensor hallucis brevis, see our post here.

As you can see, high gear is desirable over low gear push off, but sometimes circumstances or biomechanics do not permit. High gear push off ensures the forefoot is dorsiflexed and everted with respect to the rearfoot and the calcaneocuboid and talonavicular joint axes are perpendicular to one another, giving us a rigid lever to push off of as the center of gravity moves medially across the foot. In low gear push off, the foot is inverted and plantarflexed and the stress falls on the lesser metatarsals and lateral stabilizing complex of the ankle, moving the center of gravity laterally, in addition to the calcaneocuboid and subtalar joint axes being more parallel, creating a less rigid lever for push off and decreased mechanical efficiency.

If you have been following us for any length of time, you have heard us talk about how the lower kinetic chain is connected, how ankle rocker effects hip extension and how important hallux (great toe) extension is.

What can we conclude from this study?

toe spreading exercises are important for reducing navicular drop (and thus mid foot pronation, at least statically)In addition to increased abductor hallucis recruitment in ascending and descending stairs, when hip external rotation exercises were added along with toe spreading exercises folks had more recruitment of the vastus medialis (a closed chain external rotator of the leg and thigh)

Keep in mind:

the exercises given were all non weight bearing and open chain for the external rotators. Imagine what might have happened if they were both closed chain AND weight bearing!They concentrated on the effects of toe spreading (AKA lift/spread/reach) on the abductor hallucis. It also has far reaching effects on the dorsal interossei, long and short extensors of the toes.

Abstract: The purpose of the present study was to examine the effects of toe-spread (TS) exercises and hip external rotator strengthening exercises for pronated feet on lower extremity muscle activities during stair-walking. [Subjects and Methods] The participants were 20 healthy adults with no present or previous pain, no past history of surgery on the foot or the ankle, and no foot deformities. Ten subjects performed hip external rotator strengthening exercises and TS exercises and the remaining ten subjects performed only TS exercises five times per week for four weeks. [Results] Less change in navicular drop height occurred in the group that performed hip external rotator exercises than in the group that performed only TS exercises. The group that performed only TS exercises showed increased abductor hallucis muscle activity during both stair-climbing and -descending, and the group that performed hip external rotator exercises showed increased muscle activities of the vastus medialis and abductor hallucis during stair-climbing and increased muscle activity of only the abductor hallucis during stair-descending after exercise. [Conclusion] Stair-walking can be more effectively performed if the hip external rotator muscle is strengthened when TS exercises are performed for the pronated foot.

The Extensor Hallicus Brevis, or EHB as we fondly call it is an important muscle for descending the distal aspect of the 1st ray complex (1st metatarsal and medial cunieform) as well as extending the 1st metatarsophalangeal joint. It is in part responsible for affixing the medial tripod of the foot to the ground. Its motion is generally triplanar, with the position being 45 degrees from the saggital (midline) plane and 45 degrees from the frontal (coronal) plane, angled medially, which places it almost parallel with the transverse plane. With pronation, it is believed to favor adduction (1).

It arises from the anterior calcaneus and inserts on the dorsal aspect of the proximal phalynx. It is that quarter dollar sized fleshy protruding, mass on the lateral aspect of the dorsal foot. The EHB is the upper part of that mass. It is innervated by the lateral portion of one of the terminal branches of the deep peronel nerve (S1, S2), which happens to be the same as the extensor digitorum brevis (EDB), which is why some sources believe it is actually the medial part of that muscle. It appears to fire from loading response to nearly toe off, just like the EDB; another reason it may phylogenetically represent an extension of the same muscle (2-4).

Because the tendon travels behind the axis of rotation of the 1st metatarsal phalangeal joint, in addition to providing extension of the proximal phalynx of the hallux (as seen in the child above), it can also provide a downward moment on the distal 1st metatarsal (when properly coupled to and temporally sequenced with the flexor hallicus brevis and longus), assisting in formation of the foot tripod we have all come to love (the head of the 1st met, the head of the 5th met and the calcaneus).

Why is this so important?

The central axis of a joint (sometimes called the instantaneous axis of motion) is the center of movement of that articulation. It is the location where the motion will occur around, much like the center of a wheel, where the axle attaches. In an articulation, it usually involves one bone moving around another. Lets look at an example with a door hinge.

A hinge is similar to a joint, in that it has parts with is joining together (the door and the jamb), with a “joint” in between, The axis of rotation of the hinge is at the pivot rod. When the door, hinge and jamb are all aligned, it functions smoothly. Now imagine that the hinge was attached to the jamb 1/4” off center. What would happen? The hinge would bind and the door would not operate smoothly.

Now let’s think about the 1st metatarsal phalangeal joint. It exists between the head of the 1st metatarsal and the proximal part of the proximal part of the proximal phalanyx. Normally, because the head of the 1st metatarsal is larger than the heads of the lesser ones, the center of the joint is higher (actually,almost 2X as high; 8mm as opposed to 15mm). We also remember that the 1st metatarsal is usually shorter then the 2nd, meaning during a gait cycle, it bears the brunt of the weight and hits the ground earlier than the head of the 2nd.

The head of the 1st metatarsal should slide (or should we say glide?) posteriorly on the sesamoids during dorsiflexion of the hallux at pre swing (toe off). It is able to do this because of the descent of the head of the 1st metatarsal, which causes a dorsal posterior shift of the axis of rotation of the joint. We remember that the head of the 1st descends through the conjoined efforts of supination and the coordinated efforts of the peroneus longus, extensor hallucis brevis, extensor hallucis longus, dorsal and plantar interossei and flexor hallucis brevis (which nicely moves the sesamoids and keeps the process going smoothly)(1, 5).

Suffice it to say, if things go awry, the axis does not shift, the sesamoids do not move, and the phalanyx crashes into the 1st metatarsal, causing pain and if it continues, a nice spur you can write home about!

Treating and needling this muscle is easy, as it is very accessible on the dorsum of the foot and due to the decreased receptor density, is not too uncomfortable. We like to needle the peroneus longus and short flexors as well, as they all have the function of lowering the head of the 1st ray. Check it out in this quick how to video.

The Extensor Hallicus Brevis, or EHB (beautifully pictured above causing the extension (dorsiflexion) of the proximal big to is an important muscle for descending the distal aspect of the 1st ray complex (1st metatarsal and medial cunieform) as well as extending the 1st metatarsophalangeal joint.

Since this muscle is frequently dysfunctional, and is one of THE muscles than can lower the head of the 1st metatarsal, along with the peroneus longus and most likely the tibialis posterior (through its attachment to the 1st or medial cunieform), needling can often assist in normalizing function and works especially well, when coupled with an appropriate rehab program. Here is one way to needle it effectively.

One of our favorite muscles. And here it is in a recent paper! This one is for all you fellow foot geeks : )

Perhaps the FDL (which fires slightly earlier than the FHL) and FHL (which fires slightly later and longer) at loading response, slowing pronation and setting the stage for lumbrical function from midstance to terminal stance/preswing (flexion at the metatarsal phalangeal joint (it would have to be eccentric, if you think about this from a closed chain perspective) and extension (actually compression) of the proximal interphalangeal joints.

“The first lumbrical arose as two muscle bellies from both the tendon of the FDL and the tendinous slip of the FHL in 83.3 %, and as one muscle belly from the tendon of the FDL or the tendinous slip of the FHL in 16.7 %. These two muscle bellies subsequently merged to form the muscle belly of the first lumbrical. The second lumbrical arose from the tendinous slips of the FHL for the second and third toes as well as the tendon of the FDL in all specimens. The third lumbrical arose from the tendinous slips of the FHL for the third and fourth toes in 69.7 %, and the fourth lumbrical arose from the tendinous slip of the FHL for the fourth toe in 18.2 %. Some deep muscle fibers of the fourth lumbrical arose from the tendinous slip of the FHL for the second toe in 4.5 %, for the third toe in 28.8 %, and for the fourth toe in 15.2 %.”

The Gait Guys: Some strategies in Controlling the Foot Arches and Big Toe

As promised. We fixed the volume. Less hiss next time. Enjoy

Dr. Shawn Allen of The Gait Guys speaks about proper stabilization of the medial foot and arch. Muscle specifically discussed are a team: FHB (flexor hallucis brevis), AbDuctor hallucis, and tibialis posterior. He discusses the functional anatomy, normal and pathologic movement patterns of the arch and first ray complex and big toe (hallux). His foot’s ability to show the optimal patterns for the arch and hallux are excellent examples. Follow up videos and DVDs will show more details you need to know, and some of the exercises he and Dr. Ivo Waerlop use to restore a foot that has lost these abilities. The DVDs are in the works. Take their lectures and CME on www.onlineCE.com. Visit them at www.thegaitguys.com and on their facebook PAGE & Twitter of the same name for daily feeds of unique things.